Cross-linked primer composition and use thereof in thermoformable films

ABSTRACT

A primer layer and a thermoformable film that includes the primer layer are provided. The primer layer includes a cross-linked adhesive polymer having a semicrystalline region and a polar region. The cross-linked adhesive polymer has a tensile strength at maximum elongation that is less than that of an otherwise identical adhesive polymer that has not been cross-linked. The primer layer can be an outer layer of the thermoformable film, can be positioned between two additional layers of the thermoformable film, or a combination thereof. The primer layer can be positioned in contact with a mold surface during a thermoforming process.

Cross Reference to Related Applications

This application claims priority to U.S. Provisional Application Ser.No. 60/336,449, filed Oct. 31, 2001, the entire disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to primer layers and thermoformable filmsthat include the primer layers. More particularly, the primer layersinclude a cross-linked adhesive polymer having a semicrystalline regionand a polar region. The cross-linked adhesive polymer has a tensilestrength at maximum elongation that is less than that of an otherwiseidentical adhesive polymer that has not been cross-linked.

BACKGROUND OF THE INVENTION

Decorative, thermoformable films are widely used to formthree-dimensional, decorative accessories and panels that can beattached to a wide variety of industrial and consumer items such asmotor vehicles, boats, furniture, building materials, appliances, andthe like. For instance, metallized polymeric films have been used tofabricate three-dimensional objects that look as if they are made frommetal. Substitution of these objects for their metal counterparts canresult in at least one of the following: lighter weight, lowermanufacturing costs, better weather resistance, and sharper detail.

Fabricating three-dimensional objects with surfaces that look metallicis only one of many possible applications for decorative, thermoformablefilms. Many different surface effects can be incorporated into athermoformable film, and these decorative films can be used in a widevariety of applications. For example, decorative films can also be usedto provide surfaces that appear, for example, to be painted or colored,to be fluorescent or phosphorescent, or to be mirror-like orretroreflective. The surfaces can also look like wood, stone or otherceramic, parchment or other paper, or leather or other textile fabrics.The surfaces can be decorated with one or more graphic images orpatterns. WO 88/07416 and U.S. Pat. No. 6,083,335 describethermoformable films that have surfaces that appear as high glosspainted surfaces for use in the automotive industry. U.S. Pat. No.6,071,621 describes metallized polymeric films that can be used to makea wide variety of articles for automotive, furniture, and other uses.

In a conventional thermoforming process, thermoformable film is formedinto a three-dimensional shaped film and then reinforced by backfillingwith a curable fluid (e.g., a polymeric material) that hardens to form asupporting body. To improve the strength of the bond between the filmand the reinforcement, it is common for the film to have a primer layer(also referred to as a tie layer). Many kinds of conventional primerlayer compositions are known. Representative examples of conventionalprimer layer compositions include (1) a polyamide such as the materialsdescribed in EP 0,392,847 B1; (2) a hydroxy functional polymer such as ahydroxy functional polyurethane or vinyl resin (e.g., VAGH copolymeravailable from Dow Chemical); (3) a carboxyl functional polymer such asVMCH available from Dow Chemical; (4) an amine functional polymer; orcombinations thereof.

SUMMARY OF THE INVENTION

Generally, the present invention relates to primer layers and use of theprimer layers in thermoformable films. More specifically, the presentinvention provides primer layers that include a cross-linked adhesivepolymer having a semicrystalline region and a polar region. Thethermoformable films can be used in thermoforming processes not suitablefor thermoformable films having conventional primer layers.

One aspect of the invention provides a thermoformable film that includesa primer layer and at least one additional layer. The primer layerincludes a cross-linked adhesive polymer having a semicrystalline regionand a polar region. The cross-linked adhesive polymer has a tensilestrength at maximum elongation that is less than that of an otherwiseidentical adhesive polymer that has not been cross-linked. The forceneeded to elongate the cross-linked adhesive polymer to achieve goodconformance against a molding surface tends to increase very little overthe elongation ranges typically encountered in thermoforming operations.

There can be one or more primer layers included in the thermoformablefilm. For example, a first primer layer can be used as an outer layer ofthe thermoformable film and a second primer layer can be positionedbetween two additional layers of the film. The additional layers in thethermoformable film can include, but are not limited to, decorativelayers and protective layers. The primer layer can be adjacent to thedecorative layer and can be used, for example, to attach the decorativelayer to a protective layer or to attach the decorative layer toreinforcement material. The primer layer can also be used to adhere anattachment system to a thermoformed shape.

Another aspect of the invention provides a thermoformable film thatincludes at least one primer layer, a decorative layer, and atransparent, protective layer. The primer layer includes a cross-linkedadhesive polymer that can be the reaction product of co-polymerizablecompounds that include a first monomer and a second monomer. The firstmonomer is an olefinic monomer having ethylenic unsaturation. The secondmonomer includes (meth)acrylic acid, a C₁ to C₂₀ (meth)acrylate ester, a(meth)acrylate salt, acrylic acid, a C₁ to C₂₀ acrylate ester, anacrylate salt, or a combination thereof. The thermoformable film has astructure arranged in an order selected from primer layer-decorativelayer-protective layer, decorative layer-primer layer-protective layer,and primer layer-decorative layer-primer layer-protective layer.

An additional aspect of the invention provides a method of making athermoformable film. The method includes providing an adhesive polymerhaving a semicrystalline region and a polar region and having a tensilestrength at maximum elongation. The method further includescross-linking the adhesive polymer to form a cross-linked adhesivepolymer and to reduce the tensile strength at maximum elongation,preparing a primer layer that includes the cross-linked adhesivepolymer, and forming a thermoformable film that includes the primerlayer and at least one additional layer.

Another aspect of the invention provides a thermoforming method thatincludes providing a thermoformable film having a primer layer and atleast one additional layer and thermoforming the film into athree-dimensional shaped film. The primer layer includes a cross-linkedadhesive polymer having a semicrystalline region and a polar region. Theadhesive polymer has a tensile strength at maximum elongation that isless than that of an otherwise identical adhesive polymer that has notbeen cross-linked.

Yet another aspect of the invention provides a polymer layer thatincludes a cross-linked adhesive polymer having a semicrystalline regionand a polar region. The cross-linked adhesive polymer pas a tensilestrength at maximum elongation that is less than that of an otherwiseidentical adhesive polymer that has not been cross-linked.

The force needed to elongate the cross-linked adhesive polymer toachieve good conformance against a molding surface tends to increasevery little over the elongation ranges typically encountered inthermoforming operations.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The Figures and the detailed description that follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The invention can be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a plot of the force versus elongation for a semicrystalline,adhesive polymer before and after cross-linking.

FIG. 2 is a schematic cross-section of one embodiment of athermoformable film of the present invention.

FIG. 3 is a schematic diagram of one embodiment of a thermoformable filmpositioned in proximity to a male mold.

FIG. 4 is a schematic diagram of one embodiment of a thermoformed filmpositioned against molding surfaces of a male mold.

FIG. 5 is a schematic diagram of one embodiment of a male mold and athermoformed film positioned in registry with a female mold.

FIG. 6 is a schematic diagram of one embodiment, of a thermoformed filmpositioned against a female mold after transfer from a male mold.

FIG. 7 is a schematic diagram of one embodiment of a thermoformed filmpositioned against a female mold and backfilled for reinforcement.

FIG. 8 is a schematic diagram of one embodiment of an adhesive coatingand release liner provided over a backfilled, reinforced thermoformedfilm.

FIG. 9 is a schematic diagram of one embodiment of an adhesive foam tapeand a release liner provided over a backfilled, reinforced thermoformedfilm.

FIGS. 10 to 13 are differential scanning calorimeter (DSC) plots of anadhesive polymer exposed to 0, 3, 5 and 7 Mrad doses of electron beamradiation, respectively. The adhesive polymer was a copolymer ofethylene acrylic acid.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. The embodiments of the presentinvention described below are not intended to be exhaustive or to limitthe invention to the precise forms disclosed in the following detaileddescription. Rather the embodiments are chosen and described so thatothers skilled in the art may appreciate and understand the principlesand practices of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a primer layer and a thermoformable filmthat includes the primer layer and at least one additional layer. Moreparticularly, the primer layer contains a cross-linked adhesive polymerhaving a semicrystalline region and a polar region. The adhesive polymerhas a tensile strength at maximum elongation that is less than that ofan otherwise identical adhesive polymer that has not been cross-linked.

The adhesive polymers have elongation and tensile strength propertiessuitable for use in thermoforming operations. The primer layer can beused, for example, to bond one layer of a thermoformable film to anotherlayer. The primer layer can also be used to bond a surface of thethermoformable film to another material such as a reinforcementmaterial.

As used herein, the term “polymer” refers to a compound that is ahomopolymer or a copolymer. Homopolymers are typically prepared from asingle monomer or oligomer. Copolymers are typically prepared from morethan one monomers or oligomers.

As used herein, the term “semicrystalline” refers to material havingregions of crystalline and amorphous character. The term “crystalline”with respect to an adhesive polymer means that the polymer exhibits atleast some degree of macrocrystallinity, microcrystallinity, or acombination thereof. Referring to FIGS. 10-13, a polymer exhibits somedegree of macrocrystallinity if an endothermic peak E is observed in adifferential scanning calorimeter (DSC) plot, and the optical appearanceof a film, having no fillers, is cloudy or translucent. A polymerexhibits some degree of microcrystallinity if an endothermic peak E isobserved in a DSC plot and the film is clear or transparent as viewed bythe unaided eye. As can be seen in FIGS. 10-13, the endothermic peak Ecan include a shoulder portion S. In contrast, an “amorphous” materialwithout any crystalline regions typically exhibits no endothermic peakin a DSC plot and can be transparent, translucent, or opaque.

As used herein, the term “cross-linking” refers to the formation ofbonds between one polymer or portion of a polymer to another polymer orportion of a polymer. The adhesive polymers included in the primerlayers of the invention are typically cross-linked by formation of afree radical intermediate. Suitable cross-linking methods include, forexample, the use of a chemical agent, actinic radiation, and ionizingradiation.

As used herein, the “maximum percent elongation” or “E_(max)” refers toa percent elongation that is the lesser of either (i) the elongation atbreak of the polymer film or (ii) 400% elongation.

Many conventional primer layers used with thermoformable films havedrawbacks. For example, some conventional adhesive polymers do not havethe elongation and/or the tensile strength that may be desired forthermoforming processes. When incorporated as a primer layer into anotherwise thermoformable film structure, these less than desirableproperties of the adhesive polymers can adversely impact the elongationand/or tensile strength of the overall structure. As a consequence, theprimer layer properties can impair the thermoformability of the filminto deep draw shapes, can interfere with the resolution of the formedcontour, can restrict the draft angles of the contour, or can restrictthe depth to width ratio or the contour. Primer layers having morefavorable elongation and tensile strength properties are desirable forthermoforming applications.

The primer compositions of the present invention include at least onecross-linked, adhesive polymer having a semicrystalline region and apolar region. Cross-linking can modify the elongation and tensilestrength properties of the adhesive polymer. The force needed toelongate the cross-linked adhesive polymer to achieve good conformanceagainst a molding surface tends to increase very little over theelongation ranges typically encountered in thermoforming operations.Compared to adhesive polymers without cross-linking or compared toadhesive polymers having a lower amount of cross-linking, thecross-linked adhesive polymers in the primer layers of the inventiontend to have a lower tensile strength for the same percent elongation.In particular, the tensile strength at maximum elongation tends to beless. As a result of the lower tensile strength, the cross-linkedadhesive polymer can be easier to thermoform.

Thermoformable films can be prepared that include the primer layer andat least one additional layer. The primer layer can be, for example, anouter layer of the thermoformable film, positioned between twoadditional layers of the film, or a combination thereof. The propertiesof the primer layers can enhance the elongation and tensile strengthproperties of films that include the primer layer. The films can bethermoformed into articles having, for example, contours with greaterdepth to width ratios, contours with lower draft angles, and contourswith deeper draw shapes than can be obtained using conventional primers.

Some conventional primer layers have a tendency to adhere aggressivelyto a mold surface. Significant damage can occur when thermoformable filmhaving such a primer layer as an outer layer is removed from the mold.This tendency of the conventional primer layers to adhere to the moldsurface can occur even when the mold surfaces incorporate or have beentreated with a mold release agent. Direct contact between conventionalprimer layers and mold surfaces are generally avoided. However, theavoidance of direct contact between the primer layer and the moldsurfaces can limit the processes and types of molds that can be used toform three-dimensional shaped films from thermoformable films.

For example, when forming and backfilling a three-dimensional shapedfilm, the surface of the film that will be visible in the final articleis typically positioned facing the surface of a female mold. The primerlayer typically is on the opposite side of the film and does not contactthe mold surface. If a male mold rather than a female mold were used tothermoform the film into the same shape or contour, the primer layercould be in direct contact with the male mold surface. Because of thetendency of the conventional primer layers to adhere to the moldsurface, a female rather than a male mold is generally used when aprimer layer is the outer layer of the thermoformable film. This isespecially the case when the thermoforming process includes heating to atemperature that can soften the polymeric material in the primer layer.A primer layer that more easily releases from mold surfaces afterthermoforming is desirable so that the range of practical, availablemolding techniques is less restricted.

The primer layer compositions of the present invention typically are nottacky at room temperature and can have excellent mold releasecharacteristics at typical thermoforming temperatures (e.g.,temperatures in the range of room temperature up to about 120° C. or inthe range of about 60° C. to about 85° C.). Multilayered thermoformablefilms having a primer layer as an outer layer can be used in a widerange of thermoforming applications including those in which the primerlayer directly contacts a mold surface. Thus, the primer layers of thepresent invention extend the range of thermoforming operations that canbe used with primed, thermoformable films.

The thermoformable films can have any thickness suitable forthermoforming operations. In some applications, the films have athickness up to about 50 mils (about 1.27 mm) or up to about 100 mils(2.54 mm). In some embodiments, the film can have a thickness in therange of about 0.5 to about 15 mils (about 0.01 to about 3.81 mm) orabout 1 to about 5 mils (about 0.03 to about 0.13 mm); Relatively thinthermoformable films (e.g., those having a thickness up to about 50mils) are used in many thermoforming applications because such filmstend to be more conformable (i.e., more pliable, extensible, andflexible upon application of heat, pressure, and/or vacuum) and tend toexhibit more detail and more sharply defined features afterthermoforming compared to thicker film counterparts.

A thermoformable film typically possesses sufficient elongationcharacteristics to be stretched against the contours of a mold surface.The requisite degree of elongation for a film can vary from applicationto application. In some instances, the films have an elongation up toabout 15 percent, up to about 50 percent, up to about 100 percent, up toabout 200 percent, up to about 400 percent, or beyond. In someinstances, the film has elongations in the range of about-100 percent toabout 400 percent. The elongation typically is determined at atemperature where the polymer softens (e.g., temperatures up to about120° C. or in the range of about 60° C. to about 85° C.).

As used herein, a “non-self-supporting film” refers to a film that, byitself, fails to sufficiently retain its thermoformed shape when cooledand removed from a mold. The non-self-supporting film typicallycollapses upon itself. In some embodiments, a film can be deemed to benon-self-supporting if a free edge extending between adjacent corners ofa 10 cm×10 cm film sample falls more than about 3 cm below a horizontalposition relative to an opposite, supported edge of the sample extendingbetween the remaining two, adjacent corners when such opposite,supported edge of the film is held horizontally and taut at anelongation in the range from 0 to 5 percent at 25° C. In someembodiments, the film sample can fall more than about 5 cm or more thanabout 10 cm from the horizontal position. Conversely, as used herein, a“self-supporting film” refers to a film that, by itself, cansufficiently retain its thermoformed shape when cooled and removed froma mold.

Primer Layers

The primer layers of the present invention include an adhesive polymerthat is cross-linked. The adhesive polymer has a semicrystalline regionand a polar region. The polar region can provide adhesion of the primerlayer to other layers of the thermoformable film or to other materialssuch as reinforcement material. The adhesive polymer is typicallycross-linked through the semicrystalline region. In some embodiments,the adhesive polymer is cross-linked through an amorphous portion of thesemicrystalline region.

FIG. 1 compares plots of force versus percent elongation for theadhesive polymer before and after cross-linking. The tensile strength(i.e., psi) at any percent elongation can be determined by dividing theforce (i.e., pounds) by the cross-sectional area (i.e., in²) of thesample. The plots of force versus percent elongation at typicallyobtained at temperatures comparable to the mold temperature duringthermoforming processes (e.g., the mold temperature can be in the rangeof room temperature to about 120° C. or in the range of about 60° C. toabout 85° C.). The temperature used can vary depending on thecomposition of the polymeric film. Curve A is the plot obtained for afilm prepared from the adhesive polymer before cross-linking. Curve Ainitially has a relatively steep slope, indicating a high modulus, untila transition zone, or yield point C, is reached. However, even after thetransition zone C, the slope of the curve still tends to increasesignificantly with increasing elongation.

In contrast, curve B represents a plot of the force versus elongationfor a film prepared from the same adhesive polymer after cross-linking.Like curve A, curve B initially has a relatively steep slope until itstransition zone D is reached. However, after this transition zone, theslope of the curve is much flatter with increasing elongation comparedto curve A. The reduced force in curve B for a selected elongationindicates that the cross-linked adhesive polymer should be easier tothermoform than its non-cross-linked counterpart. Less force is neededto elongate the adhesive polymer after cross-linking. In particular,less force is needed subject the adhesive polymer to maximum percentelongation.

In the practice of the present invention, the tensile strength reductionfor the same percent elongation can be quantified by dividing thetensile strength at maximum percent elongation for the cross-linkedadhesive by the tensile strength at maximum percent elongation for thenon-cross-linked adhesive to obtain a tensile strength ratio. Typically,the primer layers of the present invention are characterized by atensile strength ratio of less than about 0.95. In some embodiments, thetensile strength ratio is less than about 0.85, less than about 0.75, orless than about 0.60.

Any convenient method of determining force or tensile strength versuselongation can be used as long as the same procedure is used to obtainthe data for both before and after cross-linking. According to onerepresentative approach, an elongation tester such as an Instron™tensile tester is used to determine the relationship between force ortensile strength and elongation. This specific test can be conducted,for example, using an oven fixture set at about 70° C. After clamping asample into the jaws of the tester, the jaws are separated from eachother at a controlled rate.

The primer layers of the invention containing cross-linked adhesivepolymers can have improved thermoformability compared tonon-cross-linked counterparts. When the primer layers are included inthe thermoformable film, for example, deeper draw shapes can be producedduring the thermoforming process. The result is unexpected in that onewould conventionally expect cross-linking to reduce the elongation andincrease tensile strength of a polymer, especially at elevatedtemperatures. For example, Stevens instructs that the higher thecross-link density, the greater will be the modulus (the less theelongation) in the rubbery state (see M. P. Stevens, Polymer ChemistryAn Introduction, 3^(rd) edition, Oxford University Press, p. 104(1999)). Additionally, Wicks et al. instructs that when everything elseis equal, the higher the cross-linking density, the higher the modulus.A higher modulus correlates with a harder film (see Wicks et al.,Organic Coatings: Science and Technology, Volume 1: Film formation,Components, and Appearance, John Wiley and Sons, p. 38 (1992)).

The adhesive polymers included in the primer layers can be cross-linkedusing any suitable chemical cross-linking agent, actinic radiationsource, or ionizing radiation source that can cross-link via formationof a free radical intermediate. Suitable chemical cross-linking agentsinclude, for example, peroxides and azo compounds. Suitable actinicradiation includes ultraviolet radiation from sources such as, forexample, xenon lamps, mercury vapor lamps, carbon arcs, and the like.Suitable ionizing radiation includes electron beam radiation, x-rayradiation, and gamma ray radiation.

The adhesive polymer typically contains only one type of moiety that canbe cross-linked. Adhesive polymers that are polyfunctional in terms ofcross-linking have a tendency to form polymerized networks that can betoo rigid and/or insufficiently thermoplastic in character to be usedconveniently in thermoforming operations. Additionally, excessivecross-linking can result in residual elasticity in the film that canlead to elastic recovery of the film causing loss of definition or shapein the thermoformed part.

The semicrystalline adhesive polymer can be, for example, a copolymerformed by reacting an olefinic material with a monomer having a polargroup. The olefinic portion of the adhesive polymer is typicallysemicrystalline in nature (i.e., the olefinic portion has bothcrystalline and amorphous regions). The olefinic material can be formedby free radical polymerization of monomers such as, for example,ethylene, propylene, isobutylene, or combinations thereof. In someembodiments, the olefinic material includes an olefinic monomer havingethylenic unsaturation. For example, the adhesive polymer can be acopolymer formed by reacting a polyethylene oligomer or ethylenemonomers with monomers having polar groups. The olefinic portion of theadhesive polymer can be cross-linked, for example, using electron beamradiation. In some embodiments, the adhesive polymer cross-links in anamorphous region of the olefinic portion.

The cross-linkable moiety is typically part of the semicrystallinecomponent of the adhesive polymer. For example, the polymers cancross-link by abstraction of a secondary hydrogen from an olefinicportion of the polymeric backbone. Abstraction of the hydrogen atomresults in the formation of a free radical intermediate. The freeradical intermediate can combine with other olefinic radicals oradditional polymers to form a higher molecular weight polymer. Dependingon the structure of the olefinic portion of the polymeric backbone, thefree radical intermediate can result in degradation reactions ratherthan in reactions that can increase the molecular weight bycross-linking the polymer. In some embodiments, the olefinic portionincludes polyethylene and the amount of degradation attributable toscission reactions is low.

In some embodiments, the adhesive polymers can be cross-linked usingelectron beam radiation. The appropriate radiation dosage can bedetermined through routine experimentation. The dosage can varydepending on the composition of the adhesive polymer. Some polymers aremore resistant to radiation-induced scission than other materials. Forexample, in some embodiments, the adhesive polymer contains asemicrystalline component that includes a polyolefin. Polyethylene cancross-link when exposed to electron beam radiation whereas polypropylenehas an increased tendency to undergo chain scission reactions comparedto polyethylene.

Typically, the dosage is as high as possible without unduly causing thepolymer to undergo chain scission reactions that are in excess of thecross linking reactions. Loss of molecular weight can be an indicatorthat irradiation has unduly degraded the adhesive polymer. Accordingly,for polymers that tend to undergo chain scission reactions, theradiation dosage is typically limited such that the weight averagemolecular weight of the irradiated polymer is at least about 90%, atleast about 95%, or at least about 99% of that of an otherwise identicalpolymer that has not been irradiated. The weight average molecularweight of the cross-linked adhesive polymer is preferably greater thanthe weight average molecular weight of an otherwise identical adhesivepolymer that has not been cross-linked.

In some embodiments, the electron beam radiation dosage is less thanabout 10 Mrads. For example, the dosage can be in the range of about 0.1to about 10 Mrads or in the range of about 3 to about 7 Mrads. Theradiation voltage can typically be up to about 600 kVolts. For example,the voltage can be in the range of about 25 to about 600 kVolts, about50 to about 300 kvolts, or about 100 to about at about 200 kVolts.Higher voltages can be used to penetrate a greater thickness of theadhesive polymer.

The adhesive polymers in the primer layer have a polar region. The polarregion includes polar groups that can be directly or indirectly pendantfrom the polymeric backbone or that can be part of the polymericbackbone itself. In some embodiments, the polar groups are directly orindirectly pendant from the polymer backbone. The polar groups canpromote adhesion between the adhesive polymer and a wide range of othermaterials including, for example, metal-containing compositions,ceramics, and polymeric materials having polar functionality and/orpolar chain segments, or combinations of these.

Representative examples of polar groups include acids such as sulfonic,phosphoric, phosphonic, boric, or carboxylic groups, salts based onthese acids, esters based on these acids, or combinations thereof. Thepolar groups can also include amine groups, alkoxy groups, nitrilegroups, hydroxy groups, urethane groups, quaternary ammonium groups,heterocyclic moieties such as those described in U.S. Pat. No.5,081,213, combinations of these, and the like.

The polar groups are typically incorporated in the adhesive polymer byreacting a monomer having a polar group with other monomers or oligomersthat can impart the semicrystalline characteristic to the adhesivepolymer. Representative monomers that have a polar group includeN-vinyl-2-pyrrolidone, (meth)acrylamide, acrylamide, N-substituted(meth)acrylamide, N-substituted acrylamide, nonylphenol ethoxylate(meth)acrylate, monylphenol ethoxylate acrylate, isononyl(meth)acrylate, isononyl acrylate, isobornyl (meth)acrylate, isobornylacrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate,2-(2-ethoxyethoxy)ethyl acrylate, beta-carboxyethyl (meth)acrylate,beta-carboxyethyl acrylate, maleic anhydride, itaconic acid,(meth)acrylic acid, acrylic acid, N-vinylcaprolactam, hydroxy functionalcaprolactone salt (meth)acrylate, hydroxy functional caprolactone saltacrylate, hydroxyethyl (meth)acrylate, hydroxy ethyl acrylate,hydroxymethyl (meth)acrylate, hydroxymethyl acrylate, hydroxypropyl(meth)acrylate, hydroxypropyl acrylate, hydroxyisopropyl (meth)acrylate,hydroxyisopropyl acrylate, hydroxybutyl (meth)acrylate, hydroxybutylacrylate, hydroxyisobutyl (meth)acrylate, hydroxyisobutyl acrylate,tetrahydrofurfuryl (meth)acrylate, tetrahydrofurfuryl acrylate,N-vinyl-2-pyrrolidone, diethylene glycol (meth)acrylate, diethyleneglycol acrylate, butanediol mono(meth)acrylate, butanediol nonoacrylate,(meth)acrylonitrile, acrylonitrile, beta-cyanoethyl-(meth)acrylate,beta-cyanoethyl-acrylate, 2-cyanoethoxyethyl (meth)acrylate,2-cyanoethoxyethyl acrylate, p-cyanostyrene, p-(cyanomethyl)styrene,2-hydroxyethyl (meth)acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxypropyl acrylate,1,3-dihydroxypropyl-2-(meth)acrylate, 1,3-dihydroxypropyl-2-acrylate,2,3-dihydroxypropyl-1-(meth)acrylate, 2,3-dihydroxypropyl-1-acrylate,and the like. The monomer can also include an adduct of an alpha,beta-unsaturated carboxylic acid with caprolactone, an alkanol vinylether such as 2-hydroxyethyl vinyl ether, 4-vinylbenzyl alcohol, allylalcohol, p-methylol styrene, (meth)acryloyloxyethyl trimethyl ammoniumchloride, acryloyloxyethyl trimethyl ammonium chloride,(meth)acryloyloxyethyl acid phosphate, acryloyloxyethyl acid phosphate,(meth)acrylamidopropyl trimethylammonium chloride, acrylamidopropyltrimethylammonium chloride, (meth)acryloyloxypropyldimethylbenzylammonium chloride, acryloyloxypropyldimethylbenzylammonium chloride, vinylbenzyl trimethylammonium chloride,2-hydroxy-3-allyloxypropyl trimethylammonium chloride,(meth)acrylamidopropyl sodium sulfonate, acrylamidopropyl sodiumsulfonate, sodium styrene sulfonate, styrene sulfonic acid, maleic acid,fumaric acid, maleic anhydride, vinyl sulfonic acid,2-(meth)acrylamide-2-methyl-1-propanesulfonic acid,2-acrylamide-2-methyl-1-propanesulfonic acid, dimethylaminoethyl(meth)acrylate, dimethylaminoethyl acrylate,N-(3-sulfopropyl)-N-(meth)acryloyloxyethyl-N,N-dimethylammonium betaine,N-(3-sulfopropyl)-N-acryloyloxyethyl-N,N-dimethylarnimonium betaine,2-(meth)acryloyloxyethyl trimethylammonium methosulfate,2-acryloyloxyethyl trimethylammonium methosulfate,N-(3-sulfopropyl)-N-(meth)acrylamidopropyl-N,N-dimethylammonium betaine,N-(3-sulfopropyl)-N-acrylamidopropyl-N,N-dimethylammonium betaine,vinylbenzyl trimethylammonium chloride, mixtures thereof, and the like.

In some embodiments, the polar groups are acids groups, esters thereof,or salts thereof. For example, the polar groups are carboxylic acids,carboxylate esters, or carboxylate salts. Suitable carboxylic acids,carboxylate esters, and carboxylate salts include, but are not limitedto, acrylic acid, C₁ to C₂₀ acrylate esters, acrylate salts,(meth)acrylic acid, C₁ to C₂₀ (meth)acrylate esters, (meth)acrylatesalts, or combinations thereof. Such groups typically can providesuitable adhesion to other surfaces such as polymers, metal, andcombinations thereof. Adhesive polymers having such polar groups cantypically adhere to metallized polymeric film. Primer layer compositionsthat include these polar groups can be used to adhere a metal-containinglayer to polymeric reinforcement or to protective layers, especiallypolymeric reinforcement and protective layers.

Suitable methacrylate and acrylate esters typically contain up to about20 carbon atoms or up to about 12 carbon atoms (excluding the acrlyateand methacrylate portion of the molecules). In some embodiments, themethacrylate and acrylate esters contain about 4 to about 12 carbonatoms.

In some embodiments, the adhesive polymer is a reaction product ofco-polymerizable compounds that include a first monomer that providesthat sernicrystalline region and a second monomer that provides thepolar region. For example, the first monomer can include an olefinicmonomer having ethylenic unsaturation and the second monomer can include(meth)acrylic acid, a C₁ to C₂₀ (meth)acrylate ester, a (meth)acrylatesalt, acrylic acid, a C₁ to C₂₀ acrylate ester, an acrylate salt, or acombination thereof. The adhesive polymer can be prepared using about 80to about 99 weight percent of the olefinic monomer and about 1 to about20 weight percent or the second monomer. For example, the adhesivepolymer can be prepared by copolymerizing about 83 to about 97 weightpercent of the olefinic monomer and about 3 to about 17 weight percentacrylic acid, a C₁ to C₂₀ acrylate ester, an acrylate salt,(meth)acrylic acid, a C₁ to C₂₀ (meth)acrylate ester, a (meth)acrylatesalt, or combinations thereof. In another example; the adhesive polymercontains from about 90 to about 96 weight percent of the olefinicmonomer and about 4 to about 10 weight percent acrylic acid, a C₁ to C₂₀acrylate ester, an acrylate salt, (meth)acrylic acid, a C₁ to C₂₀(meth)acrylate ester, a (meth)acrylate salt, or combinations thereof.

The positive ion of the salts typically includes alkali metal ions,alkaline earth metal ions, or transition metal ions. For example, thepositive ion can include, for example, sodium, potassium, calcium,magnesium, or zinc.

In some embodiments of the thermoformable film, the primer layerincludes an adhesive polymer such as, for example, ethylene(meth)acrylic acid or ethylene acrylic acid. Surprisingly, such primerlayer can adhere well to metal-containing layers in a thermoformablefilm while forming a surface that can be removed from a mold afterthermoforming.

Commercially available adhesive polymers are available from Dow ChemicalCo. under the trade designation “PRIMACOR.” One such copolymer isPRIMACOR 3330, which has 6.5% acrylic acid and 93.5% ethylene. Othercommercially available adhesive polymers are available from Dupont underthe trade designation “NUCREL” such as NUCREL 0403 (a copolymer ofethylene and methacrylic acid), under the trade designation “ELVALOY”(copolymers of ethylene with butyl acrylate, ethyl acrylate, or methylacrylate), and under the trade designation “SURYLN” (ionomer of ethyleneand acrylic acid).

Other suitable commercially available adhesive polymer are availablefrom Dupont under the trade designation “BYNEL” (acid modified ethylenevinyl acetate polymers) and under the trade designation “ELVAX”(ethylene vinyl acetate copolymers and ethylene/vinyl acetate/acidterpolymers).

The primer layer can also include various additives. Suitable additivesinclude, but are not limited to, antioxidants, UV stabilizers, pigments,plasticizers, gloss control agents, leveling agents, antistatic agents,bactericides, fingicides, fillers, combinations of these, and the like.

Thermoformable Films

Another aspect of the invention provides a thermoformable film thatincludes a primer layer and at least one additional layer. The primerlayer includes a cross-linked, adhesive polymer that has asemicrystalline region and a polar region. The primer layer can be anouter layer of a thermoformable film, can be one or more internal layersof a thermoformable film, or can be a combination thereof.

The primer layer can be incorporated into the thermoformable film in avariety of ways. For example, a suitable composition including theadhesive polymer and/or precursor(s) thereof can be coated fromsolution, melt, dispersion, or the like and then dried, cured, or thelike, to form a primer layer in situ. Alternatively, a primer layerincorporating the adhesive polymers can be pre-made into a film, such asby extrusion, and then adhered, laminated, or otherwise attached to oneor more other layers to form the thermoformable film. The primer layercan be cross-linked either before or after attachment to the otherlayers of the thermoformable film. In some embodiments, the primer layercan be irradiated with an electron beam to cross-link the adhesivepolymer after incorporation of the primer layer into the thermoformablefilm.

The primer layers can provide continuous, discontinuous, patterned, orrandom coverage of the surface(s) to be primed. When the primer layer isprepared in the form of a film, it can be cast, for example, on arelease liner. Suitable release liners include, but are not limited to,paper or biaxially oriented polyester itself, or biaxially orientedpolyester that has been coated on one or both sides with releasecoatings. In some embodiments, the release liner has two differentrelease coating and one of the release coatings exhibits a lower degreeof adhesion to the primer layer than the other release coating. Therelease liner can protect the surfaces of the film until it is ready tobe used.

Whether formed in situ on a surface to be primed, or pre-formed as afilm, the thickness of the primer layer typically is sufficient toimpart a desired priming effect to the surfaces that are to be bondedtogether. The thickness can vary depending on the application. In manyapplications, the thickness of the primer layers can be up to about 100micrometers. For example, the primer layer can have a thickness in therange of about 12 micrometers to about 75 micrometers or in the range ofabout 20 micrometers to about 65 micrometers. In many embodiments, thethickness is selected to achieve the desired adhesive performance at aminimal thickness. For example, the thickness can be less than about 20micrometers.

The thermoformable films of the invention can include those having adecorative surface appearance (hereinafter “decorative film”). Thedecorative films can include those having a wide variety of differentsurface appearances. For example, the surfaces can appear to be painted,to have a wood grain, to have a metallic finish such as a chrome-likefinish, to be paper or parchment, to be stone or a ceramic material, tobe leather or another textile, to have one or more graphic elements orpatters, to contain alphanumeric information, to be retroreflective ormirror-like, to be fluorescent or phosphorescent, to be glossy, mattedor otherwise textured, or to be a combination of these.

As used herein, the term “metallized polymeric film” refers to athermoformable film that includes at least one polymer layer and atleast one metal-containing layers directly or indirectly adjacent to atleast a portion of polymer layer. In some embodiments, themetal-containing layer is free of polymeric material. For example, themetal-containing layer can be a layer containing only metallicmaterials. The metal-containing layers can contain a continuous layer ofmetal or alloy bonded to or otherwise deposited on a polymeric layersuch as, for example; a protective layer. A primer or tie layer can bedisposed between the metal layer and the polymeric layer.

The various layers in the thermoformable films can be prepared from oneor more polymers and can be composites of one or more polymers withother materials. Suitable materials that can be included in compositesinclude, for example, inorganic particles or films, metals, metalalloys, pigments, passivating agents, silane compounds, metal chelates,intermetallic compositions, organic materials, conventional additives,combinations of these, and the like.

FIG. 2 schematically shows one embodiment of a thermoformable,decorative film that includes a primer layer of the present invention.The thermoformable film 50 has an outer surface 52 and an inner surface54. The outer surface 52 corresponds to the outer surface of an articleformed from the thermoformable film. Similarly, the inner surface 54corresponds to the inner surface of the article formed from thethermoformable film. The thermoformable film 50 has a multilayerconstruction that includes a decorative layer 56 with first 58 andsecond 60 major surfaces. An optional first primer layer 68 (alsoreferred to as a tie layer) overlies the first surface 58 of thedecorative layer 56. A transparent, protective layer 62 overlies theprimer layer 68. The first primer layer 68 not only helps protect thedecorative layer to some degree, but also helps adhere the film to theprotective layer 62. A second primer layer 70 can be disposed on thesecond surface 60 of the decorative layer. The second primer layer 70can promote adhesion of the decorative layer 56 to other materials suchas to an optional reinforcement or backing material (not shown), asubstrate, or the like. The first primer layer 68 and the second primerlayer 70 typically have a thickness up to about 100 micrometers. In someembodiments, the thickness can be in the range of about 5 to about 30micrometers or about 6 to about 13 micrometers. The various layers ofthe film may be formed from one or more constituent sublayers. Forexample, the transparent, protective layer 62 of this representativeembodiment includes an inner clear coat layer 64 and an outer clear coatlayer 66.

The decorative layer 56 is generally included in the thermoformable filmto provide an outer surface 52 having a desired visual appearance. Thedecorative layer is typically at least partially visually discerniblethrough the transparent, protective layer 62. The decorative layer 56can be continuous or discontinuous. In some embodiments, the decorativelayer 56 is in the form of a metal-containing layer that provides atleast a portion of the outer surface 52 of the film 50 with a metallicappearance.

In some embodiments, the metal-containing layer is opaque, highlyreflective, and/or has a polished, mirror-like finish. A typical opticaldensity of the metal layer is about 0.9 to about 3.0 as determined on aMacBeth TD 930 densitometer using a yellow filter. The metal containinglayer generally has a thickness needed to provide the desired surfaceappearance. The thickness is not so great as to adversely affect thethermoformability of decorative film. The metal-containing layertypically has a thickness in the range of about 50 to about 2500Angstroms. In some embodiments, the metal-containing layer has athickness in the range of about 300 to about 1200 Angstroms.

The metal-containing layer can be selected from a wide range ofmetal-containing materials such as, for example, metals, alloys, andintermetallic compositions. The metal-containing materials can includeone or more of tin, aluminum, indium, nickel, iron, manganese, vanadium,cobalt, zirconium, gold copper, silver, chromium, zinc, alloys thereof,combinations of these, and the like.

The transparent, protective layer 62 overlies the decorative layer 56and typically includes one or more clear coat layers (e.g., layers 64and 66 in FIG. 2). As used herein, the term “transparent” refers tomaterials that allow at least some amount of light to pass through thematerials. In some embodiments, transparent materials allow greater than50 percent, greater than 75 percent, greater than 90 percent, greaterthan 95 percent, or 100 percent of the light to pass through thematerials.

The protective layer can be formed from any of a wide variety of lighttransmissive, protective materials that also can provide the outersurface 52 of the thermoformable film 50 with one or more of thefollowing properties: abrasion resistance, high or low gloss as desired,color(s), high or low reflectivity as desired, weather resistance,heat-resistance, impact resistance, resiliency, ultra-violet resistance,protection against oxidation, water resistance, solvent resistance,and/or the like. A wide variety of protective layers are known and canbe used in the practice of the present invention. For example, oneembodiment of a transparent, protective layer includes a thermoplasticfluorinated polymer dispersed in an acrylic resin as described in U.S.Pat. No. 5,968,657. Other compositions are described in U.S. Pat. No.6,071,621. The polymers included in the protective layer can includecross-linked polymers such as, for example, a cross-linked polyurethane.

In one embodiment of a thermoformable film, the protective layer 62includes an inner 64 and an outer 66 clear coat layers. The inner clearcoat layer 64 can be used for a variety of purposes such as enhancingthe reflective, mirror-like appearance of the underlying decorativelayer, especially when the decorative layer has a metallic appearance.The inner clear coat layer 64 can be formed from a solvent castpolyurethane such as an aliphatic polyurethane. A solvent based coatingtypically provides a smooth surface on which to deposit themetal-containing layer without interfering with the overall elongationcharacteristics of the film. A solvent based coating can also helpprovide resistance to weathering when an aliphatic isocyanate isselected. The inner clear coat layer 64 typically has a thickness in therange of about 5 to about 50 micrometers.

Solvent based polyurethane precursors are commercially available fromBayer Corporation, Pittsburgh, Pa., under the trade designation“DESMOPHEN”. Suitable products include, for example, polyester polyols(e.g., product numbers product numbers 631A, 650A, 651A, 670A, 680,1100, 1150); polyether polyols (e.g. product numbers 550 U, 1600 U, 1900U, 1950 U); and acrylic polyols (e.g., product numbers A160SN, A375,A450B A/X). The clear coat may be formed from one or more polyols andreacted with an isocyanate to form a polyurethane. Isocyanates arecommercially available from Bayer Corp, under the trade designation“MONDUR” and ‘ DESMODUR” such as, for example, DESMODUR XP7100 andDESMODUR 3300.

The outer clear coat layer can be formed from a dispersion that includesaliphatic waterborne polyurethane resins such as those described in U.S.Pat. No. 6,071,621. The outer clear coat layer typically has a thicknessin the range of about 0.5 mils to about 3.0 mils. The outer clear coatprovides a protective coating that can exhibit good environmentalstability. Commercially available aliphatic waterborne polyurethanesinclude the materials from Avecia (Waalwijk in The Netherlands) underthe trade designation “NEOREZ”, such as NEOREZ XR 9699, XR 9679, and XR9603, or from Bayer, Corp. under the trade designation “BAYHDROL”, suchBAYHYDROL 121. The polyurethane compositions typically include smallamounts of a cross-linking agent, e.g., less than about 2.5%, such as adiaziridine. An example of a commercially available diaziridine isNEOCRYL CX-100 available from Avecia.

The film embodiments of FIG. 2 can be fabricated using any suitableapproach. According to one representative approach, a coatable fluidthat includes the constituents and/or precursors of the outer clear coatlayer 66 can be cast or otherwise coated onto a release liner, dried,and/or cured. The inner clear coat layer 64 can be formed over the outerclear coat layer 66 in a similar fashion from a coatable fluid thatincludes the desired constituents or precursors thereof. Next, theprimer layer 68 can optionally be disposed on the inner clear coatlayer. The primer layer can be formed by coating, lamination, or thelike. The decorative layer 56 can be coated or laminated onto the primerlayer. If the decorative layer is metallic, the metal-containing layerpreferably is formed using a suitable technique such as, for example,sputtering, vapor deposition, ion beam deposition, or chemical vapordeposition. A second primer layer 70 can be disposed on the decorativelayer. The second primer layer can be formed by coating, lamination, orthe like.

As shown in FIG. 2, the thermoformable film can contain more than oneprimer layer. In some embodiments of the thermoformable film of theinvention, only one primer layer is used. The primer layer can be, forexample, adjacent to a decorative layer. The primer layer can be oneither surface of the decorative layer. For example, the primer layercan be used to attach the decorative layer to another layer such as aprotective layer. In this example, the primer layer can be interposedbetween the decorative layer and the protective layer. In anotherexample, the primer layer can be an outer layer of a thermoformablefilm. The primer layer can be attached, for example, to a surface of adecorative layer that is not visible in the final thermoformed article.A primer layer present as an outer layer of a thermoformable film can beused, for example, to attach reinforcement material to a thermoformedshape.

In some thermoformable films that include a decorative layer, thedecorative layer can be disposed between two polymeric layers. Eachpolymeric layer can include a cross-linked polymer.

In thermoformable films that include a decorative layer and a protectivelayer, one or more primer layers can be used. For example, thethermoformable film can have a structure arranged in an order such asprimer layer-decorative layer-protective layer, decorative layer-primerlayer-protective layer, or primer layer-decorative layer-primerlayer-protective layer. In some embodiments, the protective layer andthe primer layer are both cross-linked.

Thermoforming Processes

FIGS. 3 through 9 schematically show one methodology in which thethermoformable film of the present invention can be thermoformed into athree-dimensional shaped film. Other thermoforming processes can be usedwith the primer layer and the thermoformable film of the invention.

In FIG. 3, the thermoformable film 72 is provided from a suitable supply(not shown) such as a roll or the like and positioned in operationalproximity to a male mold 74. The film 72 is generally supported in ataut state using suitable tooling such as a clamping frame 78. The outersurface of the film 80, corresponding to the visually discerniblesurface of the object to be formed, is positioned outward relative tothe male mold 74, while the backside surface 82 of the film is facingthe male mold 74 and can contact the major surface 86 of the male mold.The backside surface 82 can be a primer layer of the present invention.The male mold 74 is typically held at a suitable temperature (e.g. themold temperature it typically in the range of room temperature to about120° C. or in the range of about 60° C. to about 85° C.). Optionalheating elements (not shown), e.g., IR heaters, can also be positionedin proximity to the taut film 72 to provide additional heatingcapability if desired.

The male mold 74 includes one or more male molding surfaces (alsoreferred to in the art as “tables”) of the desired shape(s) andcontour(s). The number and relative positioning of the one or more malemold surfaces will depend upon factors including the nature of the shapebeing formed, whether the object to be formed includes one or morediscrete constituents and whether more than one such shape or article isto be thermoformed from the film at the same time. For purposes ofclarity, a single male molding surface is shown. The male moldingsurface(s) can be of varying heights, can have rounded or sharp edges,can be sloped or flat, or can have other contours as desired. As shown,male molding surface includes one or more sidewalls 84, a major topsurface 86, and transition zones 88 in the form of edges between thesidewalls and the top surface. The male mold 74 is shown with the malemold surface facing upward for purposes of illustration. In actualpractice, the male mold surface or other molds used in the thermoformingprocess can be oriented upward, toward a side, or downward as desired.

The top surface 86 can be considered the “major surface” of the mold. Asused herein, the major surface of the mold corresponds to a visuallydiscernable portion of the resulting three-dimensional object formedusing the thermoforming method. That is, the major surface (e.g., area75 in FIGS. 4 to 9) of the three-dimensional object or three-dimensionalshaped film is formed from a portion of the film 72 that contacts themale mold (i.e, the portion of the film above the major surface 86 ofthe male mold 74) prior to the initial forming of the three-dimensionalshaped film as shown in FIG. 3.

In contrast, the minor surfaces of the male mold corresponds to lessvisually discernable portion of the resulting three-dimensional shapedfilm or object formed using the thermoforming method. That is, the minorsurface of the male mold includes the sidewalls 84 as well as thesurface of the mold between the sidewalls 84 and the clamp 78. The minorsurfaces of the resulting three-dimensional shaped film orthree-dimensional object (e.g., area 76 in FIGS. 4-9) are formed fromthe portion of the film suspended over the minor surfaces of the malemold but not in contact with the male mold as shown in FIG. 3.

The male mold can include a transition region 88 that interconnect themajor and minor surfaces of the mold. In the male mold shown in thefigures, the transition region is an edge. The shape of the moldsdetermines the dimensions and geometry of the transition region. As usedherein, the transition region is typically considered part of the minorsurface.

When a thermoformable film of the invention is used in this methodology,the primer layer can be an outer layer of the film and can contact themale molding surface. In the conventional thermoforming processes, theprimer layer would not be in direct contact with any mold surface. Thus,in the conventional process, a male mold would not be used as in FIGS. 3and 4 to form a three-dimensional shaped film. With a conventionalprimer layer, the primer layer tends to aggressively adhere to any moldsurface that it contacts. It can be difficult to remove a film having aconventional primer layer from the mold without tearing the film. Theconventional primer can adhere even when the mold surface has beenprovided with a release agent.

The primer layers of the present invention have a substantially reducedtendency to stick when present on the surface of a thermoformable filmand in positioned contact with a mold surface. The primer layerstypically are not tacky at room temperature. The primer layers of theinvention can be more easily separated from the mold surface compared toconventional primers. Additionally, the primer layers of the inventioncan provide excellent coupling capabilities between materials to beadhered together, especially between metal-containing materials and/orpolymers with polar and/or hydrogen bonding functionality (e.g.,polyurethane polymers and the like).

In FIG. 4, the film 72 is conformed against the male mold surface usingconventional techniques, e.g., under pressure and/or vacuum withmoderate heating. This can be accomplished by moving the clamping frame78, the male mold 74, or both. In some embodiments, the film 72 can bebrought into contact with the male mold 74 via vacuum. Accordingly, themale mold can be porous and/or can include channels (not shown) tofacilitate such vacuum forming. In some embodiments, pressure is avoidedto minimize the risk of damaging the outer surface of the film. Thisinitial thermoforming step can be considered to be a pre-forming step.In some embodiments, the three-dimensional shaped film is furtherstretched upon being transferred to a female mold. In other embodiments,the three dimensional shaped film is not further stretched upon beingtransferred to a female mold but is transferred to a female mold tofacilitate backfilling with reinforcement material.

The thickness is not uniform across the entire three-dimensional shapedfilm. The thickness along the major surface 75 (i.e., the portion of thefilm in contact with the major surface 86 of the male mold in FIG. 4) isgreater than the average thickness along the minor surface 76 (i.e., theportion of the film adjacent to the sidewalls 84 and adjacent to themale mold surface between the sidewalls 84 and the clamp 78 in FIG. 4).In some embodiments, the three-dimensional shaped film in thinnest inthe portion positioned above the transition region 88 of the male mold90. The thickness of the film across the major surface 75 adjacent tothe major surface 86 of the male mold is substantially uniform andsubstantially equal to the thickness of the polymeric film beforethermoforming.

As used herein, the term “substantially uniform” when referring tothickness, optical density, or other physical characteristic of themajor surface of the three-dimensional shape or object means that thethickness, optical density, or other physical characteristic varies lessthan about 10 percent across the major surface. In some embodiments, thethickness, optical density, or other physical characteristic varies lessthan about 5 percent or less than 3 percent across the major surface.

As used herein, the term “substantially equal” means the property beingcompared differ by less than about 10 percent. In some embodiments, theproperty being compared differ by less than about 5 percent or less thanabout 3 percent.

The thickness can correlate with the amount of stretching that can occurin that portion of the three-dimensional shape or object during thethermoforming process. Thus, the average strain along the minor surfacesof the three-dimensional shapes or objects tends to be higher than alongthe major surface. Further, the strain across the major surface can besubstantially uniform.

Likewise, when the thermoformable film is a metallic polymeric film, thethree-dimensional shape or object typically has an average opticaldensity along the minor surfaces that is less than the optical densityalong the major surface. The optical density across the major surfacecan be substantially uniform.

The advantages of pre-forming the film 72 on a male mold can be apparenteven during the pre-forming stage. In a conventional forming process(e.g., in which a film is formed against only a female mold surfacewithout plug assistance), the portions of the film that are subjected tomaximum stretch tend to be along the top surfaces of thethree-dimensional shaped film or object. As a consequence, such surfacesmay tend to stress-whiten, crack, craze, lose brightness, lose gloss,lose reflectivity, lose color density, or the like. In the finishedarticle, these major surfaces tend to be the most visually significantin terms of affecting the overall visual appearance of the article. Lossof visual quality may be undesirable in those embodiments in which adecorative film is being used primarily to provide an article with adesired surface appearance.

In contrast, the method of the present invention protects the morevisually significant surfaces to a greater degree. The portions of thefilm that are subjected to maximum stretch are generally those formedadjacent to the minor surfaces of the male mold. In this way, the visualqualities of the major surface 75 (adjacent to the major mold surface 86of the male mold 74) of the three-dimensional shaped film can besubstantially preserved. The practical result is that this thermoformingmethod tends to shift the visual defects due to stretching to areas oflow visual significance. In the finished article, the major surfacestend to be the most visually significant in terms of affecting theoverall visual appearance of the article.

Although the minor surfaces (e.g., side surfaces and edges) typicallyexperience a greater degree of stretching than the major surface (i.e.,top surface), stretching on these surfaces can be acceptable becausethey are less visually significant compared to the more visuallysignificant major surface (i.e., top surface) in the resultantthree-dimensional object. As a consequence, the loss of reflectivity,brightness, color density, haze and the like occur across the minorsurfaces rather than across the major surface.

After the film is pre-formed against the male mold 74, thethree-dimensional shaped film 72 is transferred to a female mold 90. Thefemale mold can be held at a suitable temperature that can soften thepolymeric film (e.g., the mold temperature can be in the range of roomtemperature up to about 120° C. or in the range of about 60° C. to about85° C.). The mold, for example, can be held at a temperature sufficientto soften the polymeric material.

The transfer typically occurs directly from the male mold 74 to thefemale mold 90 as shown in FIGS. 5 and 6. Using the male mold 74 toprovide support for the film 72 during the transfer can avoid the needto use a separate, intermediate supporting member to accomplish thetransfer. Any extra transfer steps between tooling components canincrease the risk of damaging a delicate thermoformable film. Thus,supporting the pre-formed sheet upon the male mold 74 during thisportion of the transfer helps preserve the thermoformed configuration ofthe pre-formed sheet and can facilitate the use of flexible,non-supporting films in the practice of the present invention. Thisdirect transfer between the molds is particularly advantageous when thethermoformable film is a decorative, non-self-supporting film.Non-self-supporting films typically do not sufficiently retain thepre-formed shape when removed from the male mold without adequatesupport.

In FIG. 5, the male mold 74 bearing and supporting the three-dimensionalshaped film 72 is engaged in registry with a corresponding female mold90. The female mold has a major surface 96 that corresponds with themajor surface 86 of the male mold 74 and sidewalls 94 that correspondwith the sidewalls 84 of the male mold 74. Generally, the two molds arebrought into registry in a manner analogous to the way in which two diehalves of a cavity mold would be brought together. The female mold 90generally includes one or more female mold cavities respectivelycorresponding to the one or more male mold surfaces on the male mold.

When the two molds are brought together, the male mold surfaces bearingthe three-dimensional shaped film fit inside the female mold cavity. Thefemale mold cavity is over-sized relative to the male mold surfaces byat least the thickness of the film 72. The different molds are typicallysized to provide enough clearance so that the film is not unduly rubbed,abraded, torn, wrinkled, or otherwise disturbed when the two molds arebrought together. That is, the female mold cavity is typicallyover-sized enough to allow the film 72 to be positioned between themolds without damaging the film 72. The fit of the male mold surfacesand film inside the female mold cavity is close, but not snug.

In some embodiments, the female mold is sufficiently oversized relativeto the male mold such that the outer surface of the film 72 is spacedapart from the walls of the female mold cavity. This distance preferablyis not too large or too small. If the distance is too large, the majorfilm surfaces may stretch too much when transferred from the male moldto the female mold. This stretching could unduly detract from the visualappearance of these surfaces. The size of a gap between the moldsdepends on the size and shape of the objects formed. In someembodiments, the female mold can be sized to provide a gap of about 1mm. In some embodiments, the gap is less than about 0.5 mm, less thanabout 0.3 mm, or less than about 0.22 mm.

Once the female and male molds are positioned together, the pre-formedsheet 72 is transferred from the supporting male mold 74 directly to thefemale mold 90 as shown in FIG. 6. This can be accomplished using anysuitable technique such as pressure applied through the male mold and/ora vacuum through the female mold 90. In some embodiments, the use of avacuum through the female mold can minimize the risk of damaging theouter surface of the film. The female mold 90 can be porous and/orincludes channels (not shown) to facilitate such vacuum transfer if aprimer layer is an outer layer of the thermoformable film. The primerlayers of the invention can release from the male molding surface,facilitating the transfer if a primer layer is the outer layer of thethermoformable film. After the transfer is complete, the male mold 74can be withdrawn from the female mold, as shown in FIG. 6. The surface82 that was facing the male mold surface is now exposed and the surface80 that was exposed when attached to the male mold is now facing thefemale mold.

In some embodiments, when the film 72 is transferred to the female mold90, the film 72 can be subjected to additional thermoforming so as toconform to the female molding surfaces. Thus, some additional, but minorstretching of the film can occur as a consequence of the additionalthermoforming.

The degree of stretching along the major surface 75 areas of thethree-dimensional shaped film is reduced compared to a process in whicha similar shape is formed directly on the female mold withoutpre-forming on the male mold. For example, when a three-dimensionalshape is formed on a female mold without plug assist, the averagethickness variation of the film along a major surface can be about 22%.The thickness in the major surface is typically less than that of thefilm prior to thermoforming. In contrast, when using the method of thepresent invention, the average thickness variation along the majorsurface has been observed to be only about 2%. This ten-fold improvementindicates that the original thickness dimensions of the film along themajor surface are preserved to a much greater extent in the practice ofthe present invention. Because thickness reduction directly correlatesto losses of brightness, color density, reflectivity, and otherimportant visually observable properties of a film, it can beappreciated that films formed in accordance with the present inventionretain much higher levels of such qualities.

The articles prepared using the above thermoforming process can alsodiffer from articles prepared using plug assist methods. Plug-assistedthermoforming methods use a plug or plunger to push a clamped, heatedfilm into a mold. Plug-assist method tends to cause substantial, uniformstretching of the film and the overall thickness tends to be fairlyuniform across the entire thermoformed shape. The thickness along themajor surface is substantially equal to the thickness along the minorsurface. However, the thickness is typically less than the thickness ofthe film used to prepare the three-dimensional object. In contrast, themethod of the present invention produces shapes having a uniformthickness on a major surface but with thinner sections in areas thatwhere the film is stretched to conform to the mold, as shown in FIGS. 3to 8. Another distinguishing feature is that the thickness of the filmin the major surface of the three-dimensional object is about the sameas the thickness of the film prior to thermoforming.

If the thermoformed film of the present invention is sufficiently robustso as to be self-supporting, it can be cooled and removed from thefemale mold and then stored, further processed, combined with otherparts, or otherwise used as desired. However, if the thermoformed filmis of the non-self supporting type, as is the case with many embodimentsof decorative films such as metallized polymeric films, the thermoformedfilm can be reinforced before removal from the female mold. The type ofreinforcement and the methodology used to provide the reinforcement willdepend upon the nature of the shape being formed.

FIG. 7 shows one embodiment of a reinforced three-dimensional shapedfilm. Thermoformed film 72 can be backfilled with a curable fluid 100while being supported in the female mold 90 to preserve the formed shapeof the film. Backfilling can be accomplished using any suitabletechnique such as by injection molding, extruding, casting, or the like.U.S. Pat. No. 6,083,335, for example, describes a methodology in whichinjection molding is used to accomplish backfilling. However, becauseundue mold pressure can damage the visual appearance of the film, asuitably low pressure is typically used for backfilling in thoseembodiments in which visual appearance is important. In suchembodiments, the use of injection molding or extruding are typicallyavoided as these methods involve heat and pressure that could affect thesurface appearance of the film. Casting techniques can be used toreinforce the thermoformed shapes to minimize damage to the film. Afterfilling the cavity, the fluid is allowed or caused to harden into a bodythat will help support the three-dimensional object when removed fromthe mold. The primer layer helps adhere the film to the resultantreinforcing body.

The nature of the backfilling fluid can vary depending upon the desiredproperties of the resultant object. If the object is to be conformableto nonplanar surfaces, the fluid desirably cures to form an elastomericor plastically deformable material. For example, in the representativecontext in which the object is a nameplate for a vehicle, the samenameplate can be fabricated and then used on multiple types of carswhose panels have different curvatures. Distinct nameplates speciallydesigned for individual vehicles are not required. If the object is tobe attached to planar surfaces or serve a structural support function,fluids that cure to form stiffer, nonflexible bodies may be moredesirable.

Typical fluids used for backfilling reinforcement generally include oneor more polymers and/or polymer precursors. Representative examples ofthe polymers and/or resultant polymers, as the case may be, include oneor more epoxies, polyurethanes, polyimides, polyamides, polysilicones,fluoropolymers, polyesters, polyethylenes, poly(meth)acrylates,copolymers of these, and the like. In some embodiments, polyurethanepolymers, or materials that form such polymers, are preferred. Thebackfilling materials can be thermoplastic or thermosetting.Thermosetting materials that cure at temperatures below thethermoforming temperature are typically used for decorative films toavoid damaging the appearance of the film. Thermosetting polymers and/orprecursors can include one or more kinds of curing/cross-linkingfunctionality such as chemically cross-linkable functionality (e.g., theurethane linkage formed when hydroxy functionality cross-links in thepresence of polyfunctional isocyanate cross-linking agents),energy-induced cross-linking functionality (e.g., pendant (meth)acrylateor epoxy groups that cure via cationic or free radical mechanisms),combinations of these, and the like.

A variety of fluids suitable for use in backfilling are known and/orcommercially available. Representative materials suitable for use asbackfill reinforcement have been described, for example, in EP 392,847B1; U.S. Pat. No. 6,071,621; U.S. Pat. No. 5,968,657; U.S. Pat. No.4,115,619; WO 88/07416; and the like.

The mounting surface 102 of the resultant object optionally can beprovided with an attachment system. In some embodiments, the attachmentsystem includes a pressure sensitive adhesive that allows the resultantobject to be adhered and/or fastened to a desired substrate. This can beaccomplished in a variety of ways. Under one approach, as shown in FIG.8, a fluid composition that includes a pressure sensitive adhesive, orprecursor thereof, can be coated onto the mounting surface 102 and thendried or otherwise cured to provide a layer of the pressure sensitiveadhesive 104. The exposed adhesive surface can be protected with asuitable release liner 108 until used. As an option, a primer and/or tielayer or treatment (not shown) can be interposed between the mountingsurface 102 and the adhesive layer 104 to enhance adhesion to themounting surface. If used, the primer layer can be a primer layer of theinvention. Other conventional primer layers can also be used.

An alternative approach for providing the mounting surface with anattachment system is shown in FIG. 9. A double sided, adhesive foam tape112 can be applied onto the mounting surface 102. A release liner 118protects the outer adhesive surface. The release liner can be removedwhen desired to expose the adhesive surface, allowing the object to beadhered to the desired substrate. One embodiment of a double-sided,adhesive tape useful in the practice of the present invention is adouble-sided foam tape commercially available from Minnesota Mining andManufacturing Company (3M), St. Paul, Minn.

The double-sided tape can be adhered to the molded object before orafter the object is removed from the female mold. If applied before,then it is also an option to apply the tape either before or after thebackfill fluid in the cavity hardens. It is often more convenient and/ordesirable to apply the tape to the object while it is still in thefemale mold. This is more convenient, for instance, when many separateobjects in a relatively large sheet are molded at one time and will besubsequently separated from the sheet and further processed viatrimming, laser cutting, die cutting, or the like. Doing this before thefluid hardens also helps to planarize the backfill fluid in the one ormore cavities of the female mold.

Still referring to FIG. 9, an optional primer or tie layer (not shown)can be used to enhance bonding of the tape to the body. The primer layercan be formed on all or a portion of the mounting surface 102 before thetape 112 is applied. This optional primer layer can be formulated fromany suitable conventional primer composition or from a primercomposition of the invention. The resultant structure can then beremoved from the mold and then stored, cut, trimmed, further processed,combined with other parts, or otherwise used as desired in accordancewith conventional practices.

In FIGS. 4 through 9, the male and female molds, or at least the shapingsurfaces of these molds, typically include materials that exhibitrelease characteristics that allow the resultant formed film to beremoved from the mold. In some cases, a suitable material, such as afluoropolymer, silicone polymer, or the like can be integrallyincorporated into the mold. Alternatively, one or more conventional moldrelease agents can be coated onto the mold from time to time as needed.

The present invention will now be described with reference to thefollowing illustrative examples.

EXAMPLES Examples 1-4

Films were prepared by mixing the various polyurethane dispersions shownin Table 1 with about 1 weight percent cross-linking agent (NEOCRYLCX-100) based on the total solids content of the urethane dispersion,and about 10 weight percent butyl carbitol solvent. The compositionswere coated onto a release coated polyester film using conventionalmeans such as a roll coater, to form a dried film thickness of about 1mil. The coated films were dried for 2 minutes at 93° C., then for 3minutes at 140° C.

A solvent based polyol composition was formed by mixing about 10 partsof DESMOPHEN 651A65, 25 parts of DESMOPHEN 670-80, 1 part of celluloseacetate butyrate, and 58 parts of a 50/50 solvent blend of DOWANOL PMacetate and methyl isobutyl ketone (parts were based on weight). Thecomposition was stirred to mix well. To the composition was added 500parts per million of dibutyl tin dilaurate catalyst and sufficientisocyanate (DESMODUR Z4470) to obtain an isocyanate to hydroxyl ratiobetween about 0.8 and 1.2. The composition was then coated onto each ofthe dried first films using conventional means to form a dried thicknessof about 1 mil. The films were then dried and cured using a suitabletemperature profile such as for about 1.5 minutes at 150° F. (66° C.),about 1.5 minutes at 200° F. (93° C.) and about 1.5 minutes at about300° F. (149° C.).

The film with the coatings was then vapor coated with tin to an opticaldensity between about 0.9 and 3. Then a 1 mil thick layer of ethyleneacrylic acid (EAA is commercially available PRIMACOR 3330 from DowChemical Company, which has 6.5% acrylic acid and 93.5% ethylene),supported on (e.g., hot melt coated or extruded onto) a polyesterrelease film, was electron beam irradiated at 5 Mrads and 175 kVolts andthen laminated to the tin coating using a heated nip. This nip washeated to about 210° F. (99° C.). The release films were removed.

In thermoforming the film, a male mold was prepared having the letter“0” in relief. The letter had an overall size of 42 mm by 40 mm and amaximum depth of 7 mm. The width encompassed by the outside edge of the“O” and the inside edge of the “O” was about 8 mm, and the draft anglewas about 8 degrees. The film was thermoformed on the male mold bytaping the film with the EAA side against the mold. The film was heatedusing a hot air blower and the mold was heated to a temperature of about160° F. (71° C.). A vacuum of about 26 inches (66 cm) of mercury wasused to form the film after heating. After forming, the male moldbearing the formed film was placed into a corresponding female mold,heated to 160° F. (71° C.) and further formed using vacuum at about 26inches (66 cm) of mercury.

After the second forming, the thickness of the film was measured. Theoriginal film had a thickness of about 4.4 mils (0.2 mm). At the topsurface (i.e., major surface) between the inside edge and outside edgeof the “O”, the thickness was 4.2 mils (0.1 mm) using the thermoformingmethod of the invention. The top surface (i.e., major surface) exhibitedno thinning of the metal layer. Another sample of the same film wasformed only in the female mold. The thickness in the corresponding topportion was 2.8 mils, and noticeable thinning of the metal layer wasobserved.

After the female thermoforming, the molds were filled with apolyurethane reinforcing layer provided by pouring into the vacuumformed film a mixture containing equal equivalents of LEXOREZ 5901-300polysalt polyol (available from Inolex Chemical Co.), about 500 partsper million dibutyl tin dilaurate catalyst, and DESMODUR N-100polyisocyanate (available from Bayer Corp.). The mixture flowed into thecavities if the film was supported by the female mold. The heat from themold was sufficient to cause the mixture to cure.

A film such as a polyamide film (MACROMELT 6240) could be applied to theuncured urethane to promote adhesion between an adhesive tape and theurethane. A pressure sensitive tape, such as a foam tape as described inEP 392847 A2, can be attached to the polyamide film. A release liner canbe attached to the tape to protect it from dirt, or other contamination.The article can be then removed from the female mold, cooled, andfurther processed, for example die cut.

TABLE 1 Polyurethane layer combined with primer layer ExamplePolyurethane dispersion 1 BAYHYDROL 110 2 BAYHYDROL 121 3 NEOREZ XR 96994 NEOREZ XR 9603

Examples 5-7 and Comparative Example 1

A copolymer of ethylene acrylic acid (EAA), formed by reacting 93.5weight percent ethylene and 6.5 weight percent acrylic acid, wascompounded with ultraviolet stabilizers (1.35 weight percent2-(2H-benzotriazol-2-yl)4,6-di-tert-pentylphenol and 0.9 weight percent2-hydroxy-4-(octyloxy)benzophenone) and extruded as a film having athickness of 1.35 mils onto a 92 gauge polyethylene terephthalate (PET)liner. Individual EAA film samples were exposed to 3, 5, and 7 megarads(Mrads) of electron beam radiation at an accelerating voltage of 175kVolts. Comparative Example 1 had no exposure to electron beamradiation, Example 5 was exposed to 3 Mrads, Example 6 was exposed to 5Mrads, and Example 7 was exposed to 7 Mrads. Each EAA film sample wasthen cut into a 1 inch wide film strip. The PET liner was then removedand the sample was inserted into the jaws of an Instron™ tensile testingapparatus with an oven enclosure. The sample was equilibrated to atemperature of 160° F. (71° C.) prior to measuring the mechanicalproperties. The jaw separation was 2 inches and the jaw separation ratewas 12 inches/minute. The following data was recorded for the foursamples:

TABLE 2 Mechanical Properties E-beam Tensile Radiation Thickness ForceStrength Elongation Sample Dosage (inches) (lbs) (psi) (%) Comparative 0Mrads 0.00135 1.73 1287   360 Example 1 Example 5 3 Mrads 0.00135 0.83608 >400 Example 6 5 Mrads 0.00135 0.90 675 >400 Example 7 7 Mrads0.00135 0.93 680 >400

All the irradiated samples (Examples 5-7) had a lower tensile strengthat maximum elongation compared to an otherwise identical sample that hadnot been cross-linked (Comparative Example 1). The tensile strengthratio (tensile strength of the cross-linked adhesive polymer at maximumpercent elongation divided by the tensile strength of thenon-cross-linked adhesive polymer at maximum elongation) was 0.47 forExample 5, 0.52 for Example 6, and 0.53 for Example 7.

The samples included in Table 2 were also analyzed using a differentialscanning calorimeter (DSC). The samples were heated from about −50° C.to about 200° C. The DSC plots are shown in FIG. 10 for ComparativeExample 1, FIG. 11 for Example 5, FIG. 12 for Example 6, and FIG. 13 forExample 7. The DSC plots all had an endothermic peak at about 100° C.The shape of the DSC plots changed as the samples were subjected tohigher dosages of electron beam radiation. For example, the location ofthe shoulder peak S shifted with increased irradiation. The shifts inthe DSC plots confirm that the polymeric structure has been altered.

Other embodiments of this invention will be apparent to those skilled inthe art upon consideration of this specification or from practice of theinvention disclosed herein. Various omissions, modifications, andchanges to the principles and embodiments described herein may be madeby one skilled in the art without departing from the true scope andspirit of the invention which is indicated by the following claims.

1. A thermoformable film comprising a primer layer and at least oneadditional layer, said primer layer comprising a cross-linked adhesivepolymer having a semicrystalline region and a polar region, saidcross-linked adhesive polymer (i) having a tensile strength at maximumelongation that is less than that of an otherwise identical adhesivepolymer that has not been cross-linked, and (ii) being a reactionproduct of co-polymerizable compounds comprising a first monomer and asecond monomer, wherein the first monomer is an olefinic monomer havingethylenic unsaturation and the second monomer comprises acrylic acid, aC1 to C20 acrylate ester, an acrylate salt, (meth)acrylic acid, a C1 toC20 (meth)acrylate ester, a (meth)acrylate salt, or a combinationthereof; said at least one additional layer comprising an outermostprotective layer, said outermost protective layer comprisingpolyurethane or a thermoplastic fluorinated polymer.
 2. Thethermoformable film of claim 1, wherein said additional layer furthercomprises a decorative layer and wherein said primer layer is positionedadjacent to said decorative layer.
 3. The thermoformable film of claim2, wherein said decorative layer comprises a metal-containing layer. 4.The thermoformable film of claim 1, wherein said at least one additionallayer further comprises a decorative layer, wherein said decorativelayer is interposed between a first primer layer and a second primerlayer.
 5. The thermoformable film of claim 1, wherein the weight ratioof the first monomer to the second monomer is in the range of about80:20 to about 99:1.
 6. The thermoformable film of claim 1, wherein theweight ratio of the first monomer to the second monomer is in the rangeof about 90:10 to about 96:4.
 7. The thermoformable film of claim 1,wherein the cross-linked adhesive polymer comprises an ethylene acrylicacid copolymer, an ethylene (meth)acrylic acid copolymer, a combinationthereof, a C1 to C20 ester thereof, or a salt thereof.
 8. Thethermoformable film of claim 1, wherein the cross-linked adhesivepolymer is cross-linked using electron beam radiation and has a weightaverage molecular weight that is at least 90% of the weight averagemolecular weight of the otherwise identical adhesive polymer that hasnot been cross-linked.
 9. The thermoformable film of claim 1, whereinthe cross-linked adhesive polymer is cross-linked using electron beamradiation and has a weight average molecular weight that is greater thana weight average molecular weight of an otherwise identical adhesivepolymer that has not been cross-linked.
 10. The thermoformable film ofclaim 1, wherein said outermost protective layer comprises polyurethane.11. The thermoformable film of claim 10, wherein said outermostprotective layer comprises a water-based polyurethane, and saidthermoformable film further comprises a solvent-based polyurethane innerlayer positioned between said outermost protective layer and said primerlayer.
 12. A thermoformable film comprising a primer layer and at leastone additional layer, said primer layer comprising a cross-linkedadhesive polymer having a cross-linked semicrystalline region and apolar region, wherein the cross-linked adhesive polymer has a tensilestrength at maximum elongation that is less than that of an otherwiseidentical adhesive polymer that has not been cross-linked, wherein saidat least one additional layer comprises (i) a decorative layer and (ii)a protective layer that is transparent, wherein said primer layer isinterposed between said decorative layer and said protective layer. 13.The thermoformable film of claim 12, wherein the decorative layer is ametal-containing layer.
 14. The thermoformable film of claim 13, whereinthe metal-containing layer has a thickness of about 50 to about 2500Angstroms, and is formed via sputtering, vapor deposition, ion beamdeposition, or chemical vapor deposition.
 15. The thermoformable film ofclaim 12, wherein the protective layer comprises a at least onepolyurethane protective layer or a thermoplastic fluorinated polymerprotective layer.
 16. The thermoformable film of claim 12, wherein thecross-linked adhesive polymer is a reaction product of co-polymerizablecompounds comprising a first monomer and a second monomer, wherein thefirst monomer is an olefinic monomer having ethylenic unsaturation andthe second monomer comprises acrylic acid, a C1 to C20 acrylate ester,an acrylate salt, (meth)acrylic acid, a C1 to C20 (meth)acrylate ester,a (meth)acrylate salt, or a combination thereof.
 17. The thermoformablefilm of claim 12, wherein the cross-linked adhesive polymer comprises anethylene acrylic acid copolymer, an ethylene (meth)acrylic acidcopolymer, a combination thereof, a C1 to C20 ester thereof, or a saltthereof.
 18. The thermoformable film of claim 12, wherein thecross-linked adhesive polymer is cross-linked using electron beamradiation and has a weight average molecular weight that is at least 90%of the weight average molecular weight of the otherwise identicaladhesive polymer that has not been cross-linked.
 19. A thermoformablefilm comprising a primer layer and at least one additional layer, saidprimer layer comprising a cross-linked adhesive polymer having asemicrystalline region and a polar region, said cross-linked adhesivepolymer has having a tensile strength at maximum elongation that is lessthan that of an otherwise identical adhesive polymer that has not beencross-linked, wherein an exposed outer surface of said primer layer isnot tacky at room temperature, said at least one additional layercomprising (i) a decorative metal-containing layer having a thickness ofabout 50 to about 2500 Angstroms, (ii) at least one polyurethaneprotective layer or a thermoplastic fluorinated polymer protectivelayer, or (iii) both (i) and (ii).
 20. The thermoformable film of claim19, wherein said polar region comprises a carboxylic acid, a carboxylateester, a carboxylate salt, or a combination thereof.
 21. Thethermoformable film of claim 19, wherein the polar region comprises thereaction product of monomers comprising acrylic acid, an acrylate ester,an acrylate salt, (meth)acrylic acid, a (meth)acrylate ester, a(meth)acrylate salt, or a combination thereof.
 22. The thermoformablefilm of claim 19, wherein the semicrystalline region comprises apolyolefin.
 23. The thermoformable film of claim 19, wherein thecross-linked adhesive polymer comprises an ethylene acrylic acidcopolymer, an ethylene (meth)acrylic acid copolymer, a combinationthereof, a C1 to C20 ester thereof, or a salt thereof.
 24. Thethermoformable film of claim 19, wherein the cross-linked adhesivepolymer is cross-linked using electron beam radiation and has a weightaverage molecular weight that is at least 90% of the weight averagemolecular weight of the otherwise identical adhesive polymer that hasnot been cross-linked.
 25. The thermoformable film of claim 19, whereinthe cross-linked adhesive polymer is cross-linked using electron beamradiation and has a weight average molecular weight that is greater thana weight average molecular weight of an otherwise identical adhesivepolymer that has not been cross-linked.
 26. The thermoformable film ofclaim 19, wherein the at least one additional layer comprises thedecorative metal-containing layer, with the decorative metal-containinglayer being interposed between the primer layer and a protective layer.27. The thermoformable film of claim 26, wherein said decorativemetal-containing layer is formed via sputtering, vapor deposition, ionbeam deposition, or chemical vapor deposition.
 28. A thermoformable filmcomprising (1) a primer layer said primer layer comprising across-linked adhesive polymer having a semicrystalline region and apolar region, said cross-linked adhesive polymer (i) comprising areaction product of co-polymerizable compounds comprising a firstmonomer and a second monomer, wherein the first monomer is an olefinicmonomer having ethylenic unsaturation and the second monomer comprisesacrylic acid, an acrylate ester, an acrylate salt, (meth)acrylic acid, a(meth)acrylate ester, a (meth)acrylate salt, or a combination thereof,(ii) having a degree of crosslinking resulting from exposure to electronbeam radiation at a dosage ranging from about 0.1 to about 10 Mrads anda radiation voltage ranging from about 25 to about 600 kVolts, (iii)having a weight average molecular weight that is at least 90% of theweight average molecular weight of an otherwise identical adhesivepolymer that has not been cross-linked, and (iv) having a tensilestrength at maximum elongation that is less than that of an otherwiseidentical adhesive polymer that has not been cross-linked; and 2(2) atleast one additional layer comprising (i) a decorative metal-containinglayer formed via sputtering, vapor deposition, ion beam deposition, orchemical vapor deposition, (ii) at least one polyurethane protectivelayer or a thermoplastic fluorinated polymer protective layer, or (iii)both (i) and (ii).
 29. The thermoformable film of claim 28, wherein theweight ratio of the first monomer to the second monomer is in the rangeof about 80:20 to about 99:1.
 30. The thermoformable film of claim 28,wherein the weight ratio of the first monomer to the second monomer isin the range of about 90:10 to about 96:4.
 31. A method of making athermoformable film comprising: providing an adhesive polymer having atensile strength at maximum elongation and having a semicrystallineregion and a polar region; cross-linking the adhesive polymer to form across-linked adhesive polymer and to reduce the tensile strength atmaximum elongation; preparing a primer layer comprising the cross-linkedadhesive polymer; and forming a thermoformable film comprising theprimer layer and at least one additional layer, the at least oneadditional layer comprising (i) a decorative metal-containing layerhaving a thickness of about 50 to about 2500 Angstroms, (ii) at leastone polyurethane protective layer or a thermoplastic fluorinated polymerprotective layer, or (iii) both (i) and (ii).
 32. The method of claim31, wherein said cross-linking comprises forming a free radicalintermediate.
 33. The method of claim 31, wherein said cross-linkingcomprises irradiating the adhesive polymer with electron beam radiation.34. The method of claim 31, wherein the additional layer comprises thedecorative metal-containing layer, with the primer layer being adjacentto the decorative metal-containing layer.
 35. The method of claim 34,further comprising: sputtering, vapor deposition, ion beam deposition,or chemical vapor deposition the decorative metal-containing layer. 36.The method of claim 31, wherein the at least one additional layercomprises the decorative metal-containing layer and the at least onepolyurethane protective layer, with the primer layer being interposedbetween the decorative metal-containing layer and the at least onepolyurethane protective layer.
 37. The method of claim 31, wherein theat least one additional layer comprises the decorative metal-containinglayer and the at least one polyurethane protective layer, with thedecorative metal-containing layer being interposed between the primerlayer and the at least one polyurethane protective layer.
 38. A methodof forming a thermoformed article comprising: providing a thermoformablefilm formed by the method of claim 31; and thermoforming the film into athermoformed article.
 39. The method of claim 38, wherein thethermoformed article comprises a three-dimensional shaped film.
 40. Themethod of claim 39, further comprising: backfilling at least a portionof the three-dimensional shaped film so as to form a mounting surface onthe thermoformed article.
 41. The method of claim 38, furthercomprising: providing an attachment system on a surface of thethermoformed article.
 42. A method of forming a thermoformed articlecomprising: providing a thermoformable film comprising a polymer layercomprising a cross-linked adhesive polymer having a cross-linkedsemicrystalline region and a polar region, wherein (i) the polymer layerforms an exposed outer surface of the thermoformable film, (ii) thecross-linked adhesive polymer has a tensile strength at maximumelongation that is less than that of an otherwise identical adhesivepolymer that has not been cross-linked, and (iii) the cross-linkedadhesive polymer is a reaction product of co-polymerizable compoundscomprising a first monomer and a second monomer, wherein the firstmonomer is an olefinic monomer having ethylenic unsaturation and thesecond monomer comprises acrylic acid, a C1 to C20 acrylate ester, anacrylate salt, (meth)acrylic acid, a C1 to C20 (meth)acrylate ester, a(meth)acrylate salt, or a combination thereof; and thermoforming thethermoformable film in a mold to form a thermoformed article.
 43. Themethod of claim 42, wherein the thermoformed article comprises athree-dimensional shaped article.
 44. The method of claim 43, furthercomprising: backfilling at least a portion of the three-dimensionalshaped article so as to form a mounting surface on the thermoformedarticle.
 45. The method of claim 44, further comprising: providing anattachment system on the mounting surface of the thermoformed article.46. The method of claim 42, further comprising: combining a protectivelayer with the polymer layer to form the thermoformable film.
 47. Themethod of claim 46, further comprising: sputtering, vapor deposition,ion beam deposition, or chemical vapor deposition a decorativemetal-containing layer onto the protective layer.